This invention relates to a system for referencing the location of vehicles with respect to a plurality of stationary wayside stations.
There presently exists a need for a reliable economical system for periodically referencing the respective locations of a plurality of vehicles operating in the field. In general, such systems have relied upon the vehicle operator routinely advising a remote headquarters as to his geographical whereabouts. Obvious examples are the policeman in a patrol car and the cab driver. Human problems often interfere with the effectiveness of this type of system. Since people forget or neglect to report their locations, it is not uncommon for a vehicle to be "lost" for all intents and purposes since its location is unknown at a critical time. Also, emergency situations may prevent a patrolman from reporting his location at the very time that updated information as to his location may be the most critical.
Although a number of different kinds of systems have been devised which in theory provide a satisfactory vehicle location system, such systems have either been entirely too expensive for most government and private applications or they have had some inherent insurmountable problems. For example, it has been proposed heretofore to position low power transmitters at predetermined locations and have the vehicle receive a radio frequency signal when it is proximate to such transmitter indicative of the transmitter location. However, such systems have, heretofore, been impractical since the vehicle is constantly moving into and out of fringe reception areas. The number of error signals received is intolerable in these systems and obviously in many instances, inaccurate location information is worse than no information at all.